俺is a casual and assertive first-person pronoun used primarily by males. It is considered rough and informal, suitable for use with close friends or subordinates, but inappropriate in formal or polite settings.
That is how Fuguro works. It brings 俺 back for review right before you forget it, each time a little later, until it sticks for good. You hear it spoken aloud, and you meet it again in stories you can already read. The first five levels are free.